Connecting Delta Cities (english) - Rotterdam Climate Initiative

or system following the event through evacuation,
recovery, fi nancial aid and insurance relief options.
Estimates of fl ood risk and fl ood vulnerability can be
further disaggregated into vulnerability to coastal
fl oods, vulnerability to river fl oods and vulnerability
to extreme rainfall. In all three cases the impact can
be very high with numerous casualties and much
damage to property.
Extreme fl ood events are relatively rare, with typical
return periods of one hundred years and higher.
Extreme precipitation events in non-tropical cities
rarely cause casualties, but do frequently cause
damage to property and infrastructure. Tropical
cities like Hong Kong, however, have interested
historic events recorded where extreme rainfall has
caused fl ash fl ooding and mud fl ows, leading to
casualties and fl ood damage in parts of the cities.
It should be noted that vulnerability is not a static
concept. If fl ood protection is improved or evacuation
plans are developed, vulnerabilities can be reduced;
and, with expected advances in scientifi c modelling
and prediction of storms and storm surges, improved
warnings can be brought to bear in alerting
communities at risk and in managing evacuations.
Sea level rise alone may cause a presently one in a
hundred years fl ood event to occur approximately
four times more often by the end of the century.
Moreover, by the end of the 21 st century, a current
500-year fl ood event may occur approximately once
every 200 years. G4
The amount of damage from a fl ood is dependent on,
among other factors, the size of the fl ooded area and
the water depth. Other factors include the duration
of the fl ood and fl ow velocities. Furthermore, the
rate at which the water rises and the time allowed
for evacuation largely determine the number of
casualties. G7
Flood damage and infrastructure
Looking at the most important consequences of
a fl ood for diff erent economic sectors, it appears
most CDC cities are subject to similar threats from
fl ooding, both from oceanic storm surges and from
inland sources. For most ports, both land-based
transportation and the use of inland waterways
are of importance to connect the port areas with
surrounding regions. These connections may be
threatened as the clearance levels of bridges decrease
during a fl ood. Train and subway stations may be
fl ooded, coastal highways inundated, emergency
and hospital services curtailed and communications
disrupted. Furthermore, fl oods cause direct economic
damage to infrastructure and property, with the
magnitude of the damage depending on the depth
and duration of the fl ood. Most estimates of fl ood
damage rely on studies that quantify the direct
economic damages only. However, other non-fl ooded
areas may also be aff ected, as the supply of goods
and services to the fl ooded area may be hindered.
Production loss due to fl oods, however, is diffi cult to
quantify at present. Indirect fl ood damage may be
twice as high as the direct economic damage.
C L I M A T E C H A N G E I N D E L T A C I T I E S 19